Polyarylates are aromatic polyesters derived from dihydric phenols and aromatic dicarboxylic acids. The material based on 2,2-bis(4-hydroxyphenyl)propane (bisphenol-A) and a 50:50 mixture of terephthalic and isophthalic acids (1) is offered commercially by Amoco Performance Products, Inc. under the tradename of ARDEL.RTM. D-100. ##STR1## Polyarylates are high temperature, high performance thermoplastic polymers with a good combination of thermal and mechanical properties. They display excellent UV resistance and have good processibility which allows them to be molded into a variety of articles.
It is known that upon exposure to ultraviolet light polyarylates undergo the Photo-Fries rearrangement. Korshak et al., in Synthesis and Properties of Self-Protecting Polyarylates, Journal of Polymer Science, Part A-1, Vol.7, pages 157 to 172 (1969) describe a mechanism to explain what happens when polyarylates are exposed to UV light. The authors propose that polyarylates undergo the Photo-Fries rearrangement resulting in carbonyl and hydroxyl groups ortho to one another, structurally similar to o-hydroxybenzophenones which are known light absorbers. Thus, the polyarylates have increased photostability in the bulk of the material.
Cohen et al., in Transparent Ultraviolet-Barrier Coatings, Journal of Polymer Science, Part A-1, Vol. 9, pages 3263 to 3299 (1971) describe a number of phenyl polyesters, including polyarylates, which were synthesized to furnish molecules whose backbones rearrange under UV light to an o-hydroxybenzophenone structure. This Photo-Fries rearrangement -produced ultraviolet opacity in an irradiated film while maintaining visual transparency. Thin coatings of these polyesters completely protected substrates ordinarily sensitive to ultraviolet light. The authors state that spectroscopic analysis of various rearranged films and coatings showed that the o-hydroxybenzophenone polymer formed was concentrated at the irradiated surface of the original polyester coating as a "skin". Such a skin, formed in situ during the irradiation, functioned to protect both the original polyester coating as well as the coated substrate from degradation by ultraviolet irradiation. Furthermore, a significant "healing" mechanism appeared inherent in the coatings, for as the exposed skin ultimately degraded under extended ultraviolet irradiation, more of the underlying polyester layer apparently rearranged to compensate for the loss. Thus, the clear coating functioned both as a protective skin and a rearrangeable reservoir.
U.S. Pat. No. 3,492,261 describes film forming solutions of rearrangeable aromatic polyesters which are the polymeric reaction product of an aromatic dihydric compound and an aromatic dicarboxylic compound. It is stated in this patent that the preferred dihydric compounds are the ester derivatives of 4,4-bis(4'-hydroxyphenyl)pentanoic acid. The solutions of aromatic polyesters can be coated onto a substrate and dried to transparent films; they are capable of absorbing ultraviolet light and undergo rearrangement in the presence of the substrate to form a transparent compound which is stable to and will act as a barrier to ultraviolet light.
U.S. Pat. No. 3,503,779 discloses substrates which are coated with rearrangeable aromatic polyesters which are the polymeric reaction product of an aromatic dihydric compound and an aromatic dicarboxyl compound. The outer exposed surface of the aromatic polyester coatings rearrange under the influence of ultraviolet light to form a new transparent compound which is stable to and will act as a barrier to ultraviolet light.
U.S. Pat. No. 3,444,129 discloses rearrangeable aromatic polyesters which are the polymeric reaction product of an aromatic dihydric compound, and an aromatic dicarboxylic compound. The preferred dihydric compound is stated to be the ester derivatives of 4,4-bis(4'-hydroxyphenyl) pentanoic acid. The rearrangeable aromatic polyesters are useful as ultraviolet light barriers.
U.S. Pat. No. 3,460,961 describes substrates which are protected with a transparent aromatic polyester coating of two contiguous superposed layers. The aromatic polyester compounds are the reaction product of an aromatic dihydric compound and an aromatic dicarboxylic compound. The aromatic polyester coating undergoes rearrangement in the presence of ultraviolet light to form a transparent compound which is stable to and acts as a barrier to ultraviolet light.
However, in all of these references coatings are being utilized which, as discussed above, require expensive solvent coating equipment and require evaporation of a solvent.
U.S. Pat. No. 4,503,121 describes laminate compositions comprising a polyarylate, or blends thereof, derived from a dihydric phenol and an aromatic dicarboxylic acid which is laminated upon the surface of a poly(aryl ether), particularly polysulfone. It is stated therein that excellent protection is afforded the polysulfone against degradation resulting from prolonged UV exposure by laminating the polyarylate upon its surface.
Similarly, laminates formed from a layer of a polyarylate sheet and a layer of an aromatic polycarbonate, a polyester, or mixtures of these resin sheets, useful in glazing applications, are described in U.S. Pat. No. 4,643,937.
Blends containing polyarylates and polyolefins are known and are discussed in U.S. Pat. No. 4,281,079 and in U.S. patent application Ser. No. 887,434; filed on July 21, 1986 in the names of L. M. Robeson et al., titled "Blends of a Very Low Density Ethylene Polymer or Copolymer with Polyarylates and/or Polycarbonates", commonly assigned. Note that polyolefin/polyester blends have been melt-extruded into shaped articles such as filaments or films - see U.S. Pat. No. 3,534,120.
It is known that low density (.ltoreq.0.94 g/cm.sup.3) polyethylenes and EVA-modified polyethylene films are widely used as covering for greenhouses. Although UV absorbers are incorporated into the resins, the useful life of such films is usually one to two years in Florida-California outdoor exposure. Hence, laminate structures of polyarylates, which display outstanding weatherability characteristics, with polyethylenes, in which the latter would be protected against UV irradiation by a thin layer of the aromatic polyester, were deemed of utmost importance and practical interest. Such multilayer films are the subject of the instant invention.